Render only Emission data (no plane?


I have a scene of a desk that I have motion tracked and in that scene a cube with an emission material on it moves across the desk (slightly hovering above it). I would like to show the light from the cube bouncing(or sort of lightly reflecting) off the desk. I modeled a plane on the desk to catch the light from the cube and that works but I can not figure out how to remove the plane and only render the emission data. How could I go about this? Also I followed a few tutorials showing how to do a similar thing but with shadows but it didnt work, so it seems to be a different process.
Here is a video on youtube of sort of what I am trying to achieve:

any help is apreciated! thank you!

Not sure there are all nuances accounted for but hope helps.

to see only light then use a normal light source it won’t show in render
but you will see the light on desk !

emission plane will show in render
unless you remove the object in object panel

happy cl

I think he wants only the reflection almost like a shadow pass to oberlay onto footage, here’s my ugly approach using the a glossy direct pass.

rpacked.blend (758 KB)


Perfect! thank you guys this was exactly what I needed it!